The College of Medicine of the University of Iowa requests a grant for the purchase of a 137Cs source which is urgently needed to replace the obsolescent X-ray therapy-type machines presently used in the Radiation Research Laboratory as sources of radiation for research and teaching on the entire campus. The source would be of use to a large number of major users as well as other investigators. In addition, it would be of great value to predoctorals and postdoctorals in graduate programs as well as medical and radiation oncology fellows. Considering the 30 year half life of the source and the simplicity of irradiator design, the unit should be trouble-free for years to come and, therefore, serve a large number of faculty over a period of years. The unit requested would provide versatility for a large number of diverse projects. It would be possible, for example, to irradiate samples in culture flasks and petri dishes, mice and rats, large animals such as dogs, and specific regions of mammals requiring techniques involving lead shielding. The research projects in which the 137Cs source would be used immediately include selected areas of hematology, gastroenterology, immunology, neuropathology, pathology, radiology, and ophthalmology. The projects encompass a wide variety of aims and include studies of cellular control mechanisms, lymphoid cell cytotoxicity, allograft rejection, functions of T and B cells in immunoregulatory diseases, vasculitis in immune-depressed animals, repair of cerebral vasculature after freeze-injury, models of radiation-induced esophagitis and retinopathy, the role of antioxidants in mutation prevention and cancer production, changes of gut motility after irradiation, and the use of irradiated cercariae to confer immunity to mammals against a live challenge of S. japonicum. The data obtained from the investigations will have complications for diagnosis and treatment of hemopoietic and gastrointestinal disease including cancer, detection of malfunctions of the immune system, improved transplantation of tissues, and mechanisms of cell injury and repair. Thus, there should be significant contributions to the advancement of the basic and clinical sciences.